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Comment |
Folate Transport in Mouse Cumulus-Oocyte Complexes and Preimplantation Embryos. Kooistra M 2013 et al.
Endogenous folate stores are required in preimplantation embryos of several species, but how folates are accumulated and whether they can be replenished has not been determined. Folates are generally taken up into cells by specific transporters, mainly the reduced folate carrier RFC1 (SLC19A1 protein) and the high-affinity folate receptors FOLR1 and FOLR2. Quantitative RT-PCR showed that Slc19a1 mRNA was expressed in mouse cumulus-oocyte complexes (COCs) and oocytes, while Folr1 showed expression only in preimplantation embryos, increasing from the 2-cell stage onwards. mRNAs encoding Folr2 or the intestinal folate transporter Slc46a1 were not detected. Methotrexate, an antifolate often used as a model substrate for folate transport, exhibited saturable transport in COCs and in preimplantation embryos starting at the 2-cell stage. However, folate transport characteristics differed between COCs and embryos. In COCs, transport of MTX and the reduced folate leucovorin was inhibited by the anion transport inhibitor SITS that blocks RFC1 but was insensitive to dynasore, a specific dynamin inhibitor that instead inhibits folate receptor-receptor mediated endocytosis, while the opposite was found in 2-cell embryos and blastocysts. The inhibitor profile and transport properties of MTX and leucovorin in COCs correspond to established transport characteristics of the reduced folate carrier RFC1 (SLC19A1), while those in 2-cell embryos and blastocysts instead correspond with FOLR1, consistent with the mRNA expression patterns. While considerable folate was accumulated in COCs via RFC1, the presence of cumulus cells did not enhance folate accumulation in the enclosed oocyte, indicating a lack of transfer from cumulus to oocyte.
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Mutations |
1 mutations
Species: C. elegans
Mutation name: None
type: null mutation
fertility: infertile - ovarian defect
Comment: Knockout of the folate transporter folt-1 causes germline and somatic defects in C. elegans. Austin MU et al. ABSTRACT: BACKGROUND: The C. elegans gene folt-1 is an ortholog of the human reduced folate carrier gene. The FOLT-1 protein has been shown to transport folate and to be involved in uptake of exogenous folate by worms. A knockout mutation of the gene, folt-1(ok1460), was shown to cause sterility, and here we investigate the source of the sterility and the effect of the folt-1 knockout on somatic function. RESULTS: Our results show that folt-1(ok1460) knockout hermaphrodites have a substantially reduced germline, generate a small number of functional sperm, and only rarely produce a functional oocyte. We found no evidence of increased apoptosis in the germline of folt-1 knockout mutants, suggesting that germline proliferation is defective. While folt-1 knockout males are fertile, their rate of spermatogenesis was severely diminished, and the males were very poor maters. The mating defect is likely due to compromised metabolism and/or other somatic functions, as folt-1 knockout hermaphrodites displayed a shortened lifespan and elongated defecation intervals. CONCLUSIONS: The FOLT-1 protein functions in both the soma and the germline. folt-1(ok1460) hermaphrodites suffer severely diminished lifespan and germline defects that result in sterility. Germline defects associated with folate deficiency appear widespread in animals, being found in humans, mice, fruit flies, and here, nematodes.
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